In a known measuring instrument a movable instrument part is suspended by means of and between vertical tapes or strings with low torsion resistance and having low starting torque. The movable instrument part is to be influenced by the power, the effect or the like to be measured. The moving coil galvanometer is one example of such an instrument. Instrument parts suspended by tapes or strings may be used for instruments where the displaceable or rotatable part is influenced or biased without physical contact, i.e. without mechanical influence from another part. For purposes where the object to be tested or otherwise analysed is to be physically attached to the movable part or where an indicating device or the like is to be mechanically connected to a transmitter the known arrangements are hardly usable.
It has been suggested to use--for bearings where low friction and low starting torque is required--different types of magnetic bearings. DE 34 37 937 discloses a such device and more in detail a device for guiding and supporting rheological measuring systems. The intention was to bring about, in a simple way, a guiding and supporting arrangement with minimum friction and based on one stationary and one mobile magnet system with a soft iron part arranged with a vertical air gap.
Already in the 19th century however it was proved by a Mr. EARNSHAW that a devices like the one according to the DE publication is functionally impossible because of their inherent instability. It is physically impossible to achieve stability both axially and radially as is maintained in the DE publication. The device according to the DE publication not only has inferior lateral stability but is also unstable which means that it will collapse and loose its position either at the upper or the lower pair of magnets immediately.
To further clarify the state of the art and to define the invention over the state of the art, it must be mentioned that the invention is based primarily on passive magnet systems including permanent magnets only. Active magnet bearings include electromagnets shaped and arranged in a way very similar with the arrangement of a stator of a synchronous motor, whereas the armature or rotor normally is formed by a circular package of transformer sheet metal. The position of the rotor is read and checked by means of a number of distance sensors the signals from which via a quick acting boost control system optimises and distributes signals to each of the amplifier each controlling an electromagnet. In this way the rotor and shaft can be easily re-set and guided to its intended position. Annular magnet bearings, often called passive magnet bearings include annular shaped permanent magnets which attract alternatively repel each other in such a way that stability is achieved in one desired direction only, radially or axially. In the other direction, however, the bearing will always be unstable, a fact which was proven more than a hundred years ago. If ever utilized, this type of bearings always is used together with an auxiliary bearing such as an active magneto bearing.